Molecular symmetry of the ClpP component of the ATP-dependent Clp protease, an Escherichia coli homolog of 20 S proteasome.

ABSTRACT

The ClpP component Clp protease from Escherichia coli has been crystallized and examined by X-ray crystallography and self-rotation function calculations. The crystal belongs to the monoclinic space group P2(1) with unit cell dimensions of a = 196.9 A, b = 104.3 A, c = 162.4 A and beta = 98.3 degrees. The X-ray diffraction pattern extends at least to 2.5 A Bragg spacing when exposed to CuK alpha X-rays. Self-rotation function analyses indicate that the ClpP oligomer has 72-point group symmetry. This symmetry suggests that the ClpP oligomer is a tetradecamer, (ClpP)14, consisting of two heptamers, (ClpP)7 stacked on top of each other in a head-to-head fashion. The measurement of crystal density indicates that two independent copies of the ClpP oligomers are present in the asymmetric unit, giving a crystal volume per protein mass (VM) of 2.73 A3/Da and a solvent content of 54.9% (v/v). Self-rotation function calculations are consistent with the presence of two ClpP tetradecamers in the asymmetric unit. The Patterson function suggests that a translation of x = 0.5 and y = 0.5 relates a pair of ClpP oligomers in one asymmetric unit to another pair in the other asymmetric unit. And the two independent tetradecamers in one asymmetric unit are related by a relative rotation of about 18 degrees around the 7-fold axis.